Base station apparatus, mobile apparatus, and communication method

ABSTRACT

A mobile communication system includes a plurality of RAT (Radio Access Technology) and can eliminate the need of a control channel for reporting RAT information. An LTE relay station has a cover area identical to a cover area owned by a WLAN host station and relays/transmits the signal received from an LTE base station to a mobile station in the cover area of the LTE relay station. The LTE relay station adds to the signal received from the LTE base station, one of the offsets: a frequency offset, a time offset, and a power offset as information indicating that the mobile station which receives a relay signal from the local station is located in the cover area of WLAN and transmits the signal after offset addition to the mobile station located in the cover area of the LTE relay station (i.e., the cover area of WLAN).

This is a continuation application of application Ser. No. 12/669,148filed Jan. 14, 2010, which is a national stage of PCT/JP2008/001935filed Jul. 18, 2008, which is based on Japanese Application No.2007-188572 filed Jul. 19, 2007, and Japanese Application No.2007-330837 filed Dec. 21, 2007, the entire contents of each of whichare incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a relay station, mobile station andrelay transmission method in mobile communication systems.

BACKGROUND ART

In recent years, with the multimediatization of information in mobilecommunication systems, transmitting high capacity data such as stillimages and movies in addition to speech data has become popular. Torealize the transmission of high capacity data, a technology in which ahigh-frequency radio band is used to provide a high transmission rate isstudied actively.

However, when a high-frequency radio band is used, although a hightransmission rate can be expected in a short distance, attenuation dueto transmission distance becomes greater as the distance increases.Accordingly, when the mobile communication system employing ahigh-frequency radio band is operated, the coverage area of a radiocommunication base station apparatus (hereinafter “base station”)becomes small, which requires that a larger number of base stations beset up in order to prevent the service area from reducing. Since theset-up of base stations involves large costs, a technology is stronglydemanded for realizing communication services which employ ahigh-frequency radio band and preventing an increase in the number ofbase stations.

To meet this demand, to expand the coverage area of the base stations,relay transmission technologies are investigated in which a radiocommunication relay station apparatus (hereinafter “relay station”) isset up between a radio communication mobile station apparatus(hereinafter “mobile station”) and a base station, and in whichcommunication between the mobile station and the base station is carriedout via the relay station.

Meanwhile, in future mobile communication systems, combining variousradio access technologies (RATs) such as W-CDMA (Wideband Code DivisionMultiple Access), LTE (long-term evolution), WLAN (Wireless LAN), andWiMAX (Worldwide Interoperability for Microwave Access) and overlappinga plurality of RAT coverage areas in the service area of mobilecommunication will be taken into consideration. Then, in these mobilecommunication systems, a mobile station needs to detect in which RATcoverage area the mobile station is currently located and whatcommunication service the mobile station is enjoyable. For example, whenpart of an LTE coverage area includes a WLAN coverage area, a mobilestation located in the WLAN coverage area does not enjoy a WLANcommunication service unless the mobile station detects that the mobilestation is located in the WLAN coverage area, and the mobile stationenjoys an LTE communication service only.

Then, conventionally, Non-Patent Document 1 discloses a technique ofdetecting in which RAT coverage area the mobile stations are located byreporting another RAT's information (e.g. WLAN) to the mobile stationsfrom a RAT's base station (e.g. LTE) based on location information ofthe mobile stations.

-   Non-Patent Document 1: 3GPP TS 25.331 V5.19.0 (2006-12); Technical    Specification, 3rd Generation Partnership Project; Technical    Specification Group Radio Access Network; Radio Resource Control    (RRC); Protocol Specification (Release 5)

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, with the above conventional technique, a control channel forreporting information about other RATs to the mobile stations isnecessary. For example, when part of an LTE coverage area includes aWLAN coverage area, according to the above conventional technique, anLTE base station needs to report to mobile stations RAT informationabout WLAN (i.e. the information including RAT types and coverage areainformation about WLAN) using an LTE control channel. For this reason,according to the above conventional technique, a control channel oflarge capacity is necessary to report RAT information. The number ofmixed RATs is expected to further increase in the future, and thereforethere is a fear that the amount of RAT information and the frequency ofreporting RAT information increase become tight or insufficient controlchannel capacity.

It is therefore an object of the present invention to provide a relaystation, mobile station and relay transmission method that make acontrol channel for reporting RAT information unnecessary and preventcontrol channel capacity from becoming tight or insufficient in a mobilecommunication system in which a plurality of RATs mix.

Means for Solving the Problem

The relay station of the present invention adopts a configurationincluding: a receiving section that receives a signal from a basestation employing a first radio access technique and covering a firstcoverage area; an addition section that adds one of a frequency offset,a time offset and a power offset to the signal; and a transmittingsection that transmits to a mobile station the signal with the offset,in a third coverage area that is identical to a second coverage area,part or entirety of which includes the first coverage area, and which iscovered by a host station employing a second radio access techniquedifferent from the first radio access technique.

The mobile station of the present invention adopts a configurationincluding: a receiving section that receives, in a first coverage area,a signal transmitted by a base station employing a first radio accesstechnique and covering a first coverage area, and that receives a signalrelayed by a relay station in a third coverage area that is identical toa second coverage area, part or entirety of which includes the firstcoverage area, and which is covered by a host station employing a secondradio access technique different from the first radio access technique;and a detection section that detects whether or not the mobile stationis located in the second coverage area, based on which one of afrequency offset, a time offset and a power offset is added to thereceived signal.

The relay transmission method of the present invention includes stepsof: adding one of a frequency offset, a time offset and a power offsetto a signal received from a base station, employing a first radio accesstechnique and covering a first coverage area; and transmitting thesignal with one offset to a mobile station in a third coverage area thatis identical to a second coverage area, part or entirety of whichincludes the first coverage area, and which is covered by a host stationemploying a second radio access technique different from the first radioaccess technique.

Advantageous Effects of Invention

According to the present invention, in the mobile communication systemin which a plurality of RATs mix, it is possible to make a controlchannel for reporting RAT information unnecessary and prevent controlchannel capacity from becoming tight or insufficient.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration of the mobile communication systemaccording to embodiments of the present invention;

FIG. 2 is an example of transmitting and receiving a signal according toEmbodiment 1 of the present invention;

FIG. 3 is a reference table that the relay station has, according toEmbodiment 1 of the present invention;

FIG. 4 is a reference table that the mobile station has, according toEmbodiment 1 of the present invention;

FIG. 5 is a block diagram showing the configuration of the relay stationaccording to Embodiment 1 of the present invention;

FIG. 6 is a block diagram showing the configuration of the mobilestation according to Embodiment 1 of the present invention;

FIG. 7 is an example of transmitting and receiving a signal according toEmbodiment 2 of the present invention;

FIG. 8 is a reference table that the relay station has, according toEmbodiment 2 of the present invention;

FIG. 9 is a reference table that the mobile station has, according toEmbodiment 2 of the present invention;

FIG. 10 is a block diagram showing the configuration of the relaystation according to Embodiment 2 of the present invention;

FIG. 11 is a block diagram showing the configuration of the mobilestation according to Embodiment 2 of the present invention;

FIG. 12 is an example of transmitting and receiving a signal accordingto Embodiment 3 of the present invention;

FIG. 13 is a reference table that the relay station has, according toEmbodiment 3 of the present invention;

FIG. 14 is a reference table that the mobile station has, according toEmbodiment 3 of the present invention;

FIG. 15 is a block diagram showing the configuration of the relaystation according to Embodiment 3 of the present invention; and

FIG. 16 is a block diagram showing a configuration of the mobile stationaccording to Embodiment 3 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

FIG. 1 shows a mobile communication system according to embodiments ofthe present invention. As shown in FIG. 1, with the mobile communicationsystem according to the following embodiments, part of LTE coverage area11 (i.e. coverage area of a wideband communication system) includes anentire WLAN coverage area 21 (i.e. coverage area of a narrowbandcommunication system). That is, part of LTE coverage area 11 overlapsentire WLAN coverage area 21.

LTE base station 10, which covers coverage area 11, transmits a signalin this coverage area 11. This signal is received by LTE relay station30 and mobile station 40. LTE relay station 30 covers identical coveragearea 31 to coverage area 21, which WLAN host station 20 has, and relays,in coverage area 31, the signal received from LTE base station 10 tomobile station 40. That is, LTE relay station 30 relays a signal of LTEin WLAN coverage area 21 only. Therefore, mobile station 40 directlyreceives a signal transmitted by LTE base station 10 in coverage area11, and receives a signal relayed by LTE relay station 30 in coveragearea 31 (i.e. coverage area 21).

To make coverage area 31 and coverage area 21 identical, it ispreferable to position LTE relay station 30 in an identical place toWLAN host station 20.

Further, LTE relay station 30 adds, to the relay signal, information toshow that mobile station 40 receiving the relay signal from LTE relaystation 30, is located in WLAN coverage area 21. To be more specific,LTE relay station 30 adds either a frequency offset, a time offset or apower offset, as the above information to the signal received from LTEbase station 10, and transmits the signal with the offset to mobilestation 40, located in coverage area 31 (that is, coverage area 21).This process of adding an offset is performed in a lower layer thanlayer 1.

That is, mobile station 40 can decide whether or not the mobile station40 is located in WLAN coverage area 21 based on which one of the aboveoffsets is added to a received signal. Consequently, mobile station 40can enjoy a WLAN communication service when mobile station 40 is locatedin coverage area 21 within coverage area 11.

Embodiment 1

With the present embodiment, a case will be described where a frequencyoffset is added to a signal subject to relay.

With the present embodiment, as shown in FIG. 2, LTE base station 10transmits a signal having a center frequency f_(C).

When LTE relay station 30 receives the signal from LTE base station 10and relays the signal to mobile station 40, LTE relay station 30 addsfrequency offset Δf to the signal from LIE base station 10, to shift thecenter frequency to f_(R). The magnitude of Δf varies between RATscovering an identical coverage area to coverage area 31 of LTE relaystation 30. For example, if coverage area 31 of LTE relay station 30 isidentical to WLAN coverage area 21 as shown in FIG. 1, Δf is 30 kHz asshown in FIG. 3. Further, for example, if coverage area 31 of LTE relaystation 30 is identical to a WiMAX coverage area, Δf is 60 kHz as shownin FIG. 3. Then, LTE relay station 30 relays the signal having centerfrequency f_(R) to mobile station 40.

Mobile station 40 decides in which RAT coverage area mobile station 40is located based on whether or not frequency offset Δf is added to thereceived signal.

Mobile station 40, located in the overlapping part of LTE coverage area11 and another RAT coverage area, receives both the signal having centerfrequency f_(C) and transmitted by LTE base station 10 and the signalhaving center frequency f_(R) and relayed by LTE relay station 30.Accordingly, mobile station 40, located in overlapping part of LTEcoverage area 11 and another RAT coverage area, can detect frequencyoffset Δf=|f_(R)−f_(C)| added by LTE relay station 30. For example, asshown in FIG. 4, when Δf having a range of 29 to 31 kHz is added to areceived signal, mobile station 40 detects that mobile station 40 islocated in WLAN coverage area 21 and can enjoy both WLAN and LTEcommunication services. Further, for example, as shown in FIG. 4, whenΔf having a range of 59 to 61 kHz is added to a received signal, mobilestation 40 detects that mobile station 40 is located in the WiMAXcoverage area and can enjoy both WiMAX and LIE communication services.

On the other hand, mobile station 40, located outside the aboveoverlapping part in LTE coverage area 11, receives only the signalhaving center frequency f_(C) and transmitted by LTE base station 10.Accordingly, mobile station 40, located outside the above overlappingpart in LTE coverage area 11, cannot detect frequency offset Δf havingthe ranges shown in FIG. 4. For example, when Δf having the ranges shownin FIG. 4 is not added to a received signal, mobile station 40 detectsthat mobile station 40 is not located in WLAN coverage area 21 or in theWiMAX coverage area and can enjoy LTE communication service only. Thatis, when frequency offset Δf is not added to a received signal, mobilestation 40 can decide that mobile station 40 is located outside thecoverage area of a narrowband communication system.

Next, an optimal value of frequency offset Δf will be explained.

in LTE, when the maximum downlink carrier frequency is 2690 MHz and themaximum moving speed of a mobile station is 350 km/h, the maximumfrequency error due to crystal error in the mobile station upondetecting a coverage area (i.e. upon acquiring initial synchronization)is estimated, for example, ±5 ppm. This maximum frequency error refersto an error in the initial status of the crystal provided in the mobilestation, that is, an error before performing synchronizationacquisition. Accordingly, the maximum Doppler shift due to fading is 872Hz and the maximum frequency error due to crystal error is 13450 Hz.Accordingly, the maximum frequency error f_(error) _(—) _(max)=(themaximum Doppler shift due to fading+the maximum frequency error due tocrystal error)=14322 Hz≈14 kHz. Therefore, the value of frequency offsetΔf added by LTE relay station 30 needs to be within the range off_(detect) that can be detected in mobile station 40 and separatablefrom the maximum frequency error f_(error) _(—) _(max)≈14 kHz. That is,to make detection easier, it is preferable that the value of Δf meetsboth condition (1) Δf≦f_(detect)−f_(error) _(—) _(max) and condition (2)Δf>2*f_(error) _(—) _(max). Then, with the present embodiment, as shownin FIG. 3, Δf in WLAN is 30 kHz and Δf in WiMAX is 60 kHz.

Next, the configuration of LTE relay station 30 according to the presentembodiment will be described. FIG. 5 shows the configuration of LTErelay station 30 according to the present embodiment.

In LTE relay station 30 shown in FIG. 5, radio receiving section 302receives a signal transmitted from LTE base station 10 via antenna 301,and performs receiving processing including down-conversion and A/Dconversion on the received signal, to output the resulting signal tofrequency offset addition section 304.

Offset determination section 303, which has the table shown in FIG. 3,determines frequency offset Δf with reference to the table shown in FIG.3 according to RAT type information received as input. If the RAT typeis WLAN, Δf is determined to be 30 kHz. Further, if the RAT type isWiMAX, Δf is determined to be 60 kHz. If LTE relay station 30 isconnected to a host station of a narrowband communication system thatcovers an identical coverage area to LTE relay station 30 (e.g. WLANhost station 20 in FIG. 1) via a wired connection, LTE relay station 30acquires RAT type information from the host station. Δf determined inoffset determination section 303 is inputted to frequency offsetaddition section 304.

Frequency offset addition section 304 adds Δf determined in offsetdetermination section 303 to the signal received as input from radioreceiving section 302, and outputs the signal with the frequency offsetto radio transmitting section 305.

Radio transmitting section 305 performs transmitting processingincluding D/A conversion and up-conversion on the signal with thefrequency offset, and relays the resulting signal from antenna 301 tomobile station 40.

Next, the configuration of mobile station 40 according to the presentembodiment will be described. FIG. 6 shows the configuration of mobilestation 40 according to the present embodiment.

In mobile station 40 shown in FIG. 6, radio receiving section 402receives only a signal from LTE base station 10, or a signal from LTEbase station 10 and a signal from LTE relay station 30 via antenna 401,and performs receiving processing including down-conversion and A/Dconversion on each received signal, to output the resulting signal tofrequency error compensation section 403, frequency error detectionsection 494 and frequency offset detection section 405.

Frequency error detection section 404 detects a frequency errorf_(error) of the received signal=(Doppler shift due to fading+thefrequency error due to crystal error) and outputs the detected frequencyerror to frequency error compensation section 403 and frequency offsetdetection section 405.

Frequency error compensation section 403 compensates for the frequencyerror f_(error) of the received signal and outputs the signal after thefrequency error compensation to demodulation section 407 and frequencyoffset compensation section 408.

Demodulation section 407 demodulates the signal after frequency errorcompensation and outputs the demodulated signal to diversity combinationsection 410.

Frequency offset detection section 405 detects frequency offsetΔf=|f_(R)−f_(C)| with the received signal. The detected Δf is inputtedto RAT detection section 406 and frequency offset compensation section408.

Frequency offset compensation section 408 further compensates for thefrequency offset Δf with the signal after frequency error compensationand outputs the signal after frequency offset compensation, todemodulation section 409.

Demodulation section 409 demodulates the signal after the frequencyerror compensation and the frequency offset compensation, and outputsthe demodulated signal to diversity combination section 410.

Diversity combination section 410 diversity-combines the signal receivedas input from demodulation section 407 and the signal received as inputfrom demodulation section 409 and outputs a combined signal.

RAT detection section 406, which has the table shown in FIG. 4 detectsin which RAT coverage area mobile station 40 is located as describedabove, with reference to the table shown in FIG. 4 according to Δfdetected by frequency offset detection section 405. Then, RAT detectionsection 406 outputs a RAT detection result.

Embodiment 2

With the present embodiment, a case will be described where a timeoffset is added to a signal subject to relay.

With the present embodiment, as shown in FIG. 7, LTE relay station 30receives a signal having a peak at time t₀ from LTE base station 10.

When LTE relay station 30 receives the signal from LTE base station 10and relays the signal to mobile station 40, LTE relay station 30 addstime offset ΔT to the signal from LTE base station 10, to generate asignal having a peak at time t₁. The magnitude of ΔT varies between RATscovering an identical coverage area to coverage area 31 of LTE relaystation 30. For example, if coverage area 31 of LTE relay station 30 isidentical to WLAN coverage area 21 as shown in FIG. 1, ΔT is 5 samplesas shown in FIG. 8. Further, for example, if coverage area 31 of LTErelay station 30 is identical to a WiMAX coverage area, ΔT is 10 samplesas shown in FIG. 8. Then, LTE relay station 30 relays the signal havingthe time offset ΔT and the peak at time t₁ to mobile station 40.

Mobile station 40 decides in which RAT coverage area mobile station 40is located based on whether or not time offset ΔT is added to thereceived signal.

Mobile station 40, which is located in overlapping part of LTE coveragearea 11 and another RAT coverage area, receives both the signal having apeak at time t₀ and transmitted by LTE base station 10 and the signalhaving a peak at time t₁ and relayed by LTE relay station 30.Accordingly, mobile station 40, which is located in overlapping part ofLTE coverage area II and another RAT coverage area, can detect timeoffset ΔT=|t₁−t₀| added by LTE relay station 30. For example, as shownin FIG. 9, when ΔT having a range of 3 to 7 samples is added to areceived signal, mobile station 40 detects that mobile station 40 islocated in WLAN coverage area 21 and can enjoy both WLAN and LTEcommunication services. Further, for example, as shown in FIG. 9, whenΔT having a range of 8 to 12 samples is added to a received signal,mobile station 40 detects that mobile station 40 is located in the WiMAXcoverage area and can enjoy both WiMAX and LTE communication services.

On the other hand, mobile station 40, located outside the aboveoverlapping part in LTE coverage area 11, receives only the signalhaving a peak at time t₀ and transmitted by LTE base station 10.Accordingly, mobile station 40, located outside the above overlappingpart in LTE coverage area 11, cannot detect time offset ΔT having theranges shown in FIG. 9. For example, when ΔT having the ranges shown inFIG. 9 is not added to a received signal, mobile station 40 detects thatmobile station 40 is not located in WLAN coverage area 21 or in theWiMAX coverage area and can enjoy LTE communication service only. Thatis, when time offset ΔT is not added to a received signal, mobilestation 40 can decide that mobile station 40 is located outside thecoverage area of a narrowband communication system.

In LTE, usually, a guard interval T_(guard) is set based on several tensto hundreds of samples, taking into consideration of the maximum delaytime of a multipath T_(delay) _(—) _(max). That is, to make detectioneasier, it is preferable that the value of time offset ΔT added by LTErelay station 30, meets the condition ΔT≦T_(guard)−T_(delay) _(—)_(max).

Next, the configuration of LTE relay station 30 according to the presentembodiment will be described. FIG. 10 shows the configuration of LIErelay station 30 according to the present embodiment. Further, in FIG.10 the same reference numerals are assigned to the same parts in FIG. 5(Embodiment 1), and description thereof will be omitted.

In LTE relay station 30 shown in FIG. 10, offset determination section306, which has the table shown in FIG. 8 determines time offset ΔT withreference to the table shown in FIG. 8 according to RAT type informationreceived as input. If the RAT type is WLAN, ΔT is determined to be 5samples. Further, if the RAT type is WiMAX, ΔT is determined to be 10samples. If LTE relay station 30 is connected to a host station of anarrowband communication system that covers an identical coverage areato LTE relay station 30 (e.g. WLAN host station 20 in FIG. 1) via awired connection, LTE relay station 30 acquires RAT type informationfrom the host station. ΔT determined in offset determination section 306is inputted to time offset addition section 307.

Time offset addition section 307 adds ΔT determined in offsetdetermination section 306 to the signal received as input from radioreceiving section 302, and outputs the signal with the time offset toradio transmitting section 305.

Next, the configuration of mobile station 40 according to the presentembodiment will be described. FIG. 11 shows the configuration of mobilestation 40 according to the present embodiment. Further, in FIG. 11 thesame reference numerals are assigned to the same parts in FIG. 6(Embodiment 1), and description thereof will be omitted.

In mobile station 40 shown in FIG. 11, radio receiving section 402receives only a signal from LTE base station 10, or a signal from LTEbase station 10 and a signal from LTE relay station 30 via antenna 401,and performs receiving processing including down-conversion and A/Dconversion on each received signal, to output the resulting signal totime error compensation section 411, time error detection section 412and time offset detection section 413.

Time error detection section 412 detects time error of the receivedsignal by the channel and outputs the detected time error to time errorcompensation section 411 and time offset detection section 413.

Time error compensation section 411 compensates for the time error ofthe received signal by the channel and outputs the signal after the timeerror compensation, to demodulation section 415 and time offsetcompensation section 416.

Demodulation section 415 demodulates the signal after time errorcompensation and outputs the demodulated signal to diversity combinationsection 410.

Time offset detection section 413 detects time offset ΔT=|t₁−t₀| withthe received signal. The detected ΔT is inputted to RAT detectionsection 414 and time offset compensation section 416.

Time offset compensation section 416 further compensates for the timeoffset ΔT with the signal after time error compensation and outputs thesignal after time offset compensation, to demodulation section 417.

Demodulation section 417 demodulates the signal after time errorcompensation and time offset compensation and outputs the demodulatedsignal to diversity combination section 410.

Diversity combination section 410 diversity-combines the signal receivedas input from demodulation section 415 and the signal received as inputfrom demodulation section 417 and outputs a combined signal.

RAT detection section 414, which has the table shown in FIG. 9 detectsin which RAT coverage area mobile station 40 is located, as describedabove, with reference to the table shown in FIG. 9 according to ΔTdetected by time offset detection section 413. Then, RAT detectionsection 414 outputs a RAT detection result.

Embodiment 3

With the present embodiment, cases will be described where a poweroffset is added to a signal subject to relay.

With the present embodiment, as shown in FIG. 12, LTE base station 10transmits a signal having power P₀.

When LTE relay station 30 receives a signal from LTE base station 10 andrelays the signal to mobile station 40, LTE relay station 30 adds poweroffset ΔP to part of the signal from LTE base station 10, to generate asignal having power P₀ and P₁. The magnitude of ΔP varies between RATscovering an identical coverage area to coverage area 31 of LTE relaystation 30. For example, if coverage area 31 of LTE relay station 30 isidentical to WLAN coverage area 21 as shown in FIG. 1, ΔP is −3 dB asshown in FIG. 13. Further, for example, if coverage area 31 of LTE relaystation 30 is identical to a WiMAX coverage area, ΔP is +5 dB as shownin FIG. 13. Then, LTE relay station 30 relays the signal with poweroffset. ΔP to mobile station 40.

Mobile station 40 detects in which RAT coverage area mobile station 40is located based on whether or not power offset ΔP is added to thereceived signal.

Mobile station 40, located in the overlapping part of LTE coverage area11 and another RAT coverage area, receives both the signal having powerP₀ and transmitted by LTE base station 10 and the signal having power P₀and P₁ and relayed by LTE relay station 30. Accordingly, mobile station40, located in overlapping part of LTE coverage area 11 and another RATcoverage area, can detect power offset ΔP=|P₁−P₀| added by LTE relaystation 30. For example, as shown in FIG. 14, when ΔP having a range of−5 to −1 dB is added to a received signal, mobile station 40 detectsthat mobile station 40 is located in WLAN coverage area 21 and can enjoyboth WLAN and LTE communication services. Further, for example, as shownin FIG. 14, when ΔP having a range of +3 to +7 dB is added to a receivedsignal, mobile station 40 detects that mobile station 40 is located inthe WiMAX coverage area and can enjoy both WiMAX and LTE communicationservices.

On the other hand, mobile station 40, located outside the aboveoverlapping part in LIE coverage area 11, receives only the signalhaving power P₀ and transmitted by LTE base station 10. Accordingly,mobile station 40, located outside the above overlapping part in LTEcoverage area 11, cannot detect power offset ΔP having the ranges shownin FIG. 14. For example, when ΔP having the ranges shown in FIG. 14 isnot added to a received signal, mobile station 40 detects that mobilestation 40 is not located in WLAN coverage area 21 or in the WiMAXcoverage area and can enjoy LTE communication service only. That is,when power offset ΔP is not added to a received signal, mobile stationcan decide that mobile station 40 is located outside the coverage areaof a narrowband communication system.

In LTE, received dynamic range P_(total) is usually set by adding amargin to dynamic range P_(fading) estimated using fading fluctuations.That is, to make detection easier, it is preferable that the value ofpower offset ΔP is added by LTE relay station 30, meets the conditionΔP≦P_(total)−P_(fading).

Next, the configuration of LTE relay station 30 according to the presentembodiment will be described. FIG. 15 shows the configuration of LTErelay station 30 according to the present embodiment. Further, in FIG.15 the same reference numerals are assigned to the same parts in FIG. 5(Embodiment 1), and description thereof will be omitted.

In LTE relay station 30 shown in FIG. 15, offset determination section308, which has the table shown in FIG. 13 determines power offset ΔPwith reference to the table shown in FIG. 13 according to RAT typeinformation received as input. If the RAT type is WLAN, ΔP is determinedto be −3 dB. Further, if the RAT type is WiMAX, ΔP is determined to be+5 dB. If LTE relay station 30 is connected to a host station of anarrowband communication system that covers an identical coverage areato LTE relay station 30 (e.g. WLAN host station 20 in FIG. 1) via awired connection, LTE relay station 30 acquires RAT type informationfrom the host station. ΔP determined in offset determination section 308is inputted to power offset addition section 309.

Power offset addition section 309 adds ΔP determined in offsetdetermination section 308 to part of the signal received as input fromradio receiving section 302, and outputs the signal with the poweroffset to radio transmitting section 305.

Next, the configuration of mobile station 40 according to the presentembodiment will be described. FIG. 16 shows the configuration of mobilestation 40 according to the present embodiment. Further, in FIG. 16 thesame reference numerals are assigned to the same parts in FIG. 6(Embodiment 1), and description thereof will be omitted.

In mobile station 40 shown in FIG. 16, radio receiving section 402receives only a signal from LTE base station 10, or a signal from LTEbase station 10 and a signal from LTE relay station 30 via antenna 401,and performs receiving processing including down-conversion and A/Dconversion on each received signal, to output the resulting signal topower offset detection section 418, demodulation section 420 and poweroffset compensation section 421.

Demodulation section 420 demodulates the received signal and outputs thedemodulated signal to diversity combination section 410.

Power offset detection section 418 detects power offset ΔP=|P₁−P₀| withthe received signal. The detected ΔP is inputted to RAT detectionsection 419 and power offset compensation section 421.

Power offset compensation section 421 compensates for the power offsetΔP with the received signal and outputs the signal after power offsetcompensation, to demodulation section 422.

Demodulation section 422 demodulates the signal after power offsetcompensation and outputs the demodulated signal to diversity combinationsection 410.

Diversity combination section 410 diversity-combines the signal receivedas input from demodulation section 420 and the signal received as inputfrom demodulation section 422 and outputs a combined signal.

RAT detection section 419, which has the table shown in FIG. 14, anddetects in which RAT coverage area mobile station 40 is located asdescribed above, with reference to the table shown in FIG. 14 accordingto the ΔP detected by power offset detection section 418. Then, RATdetection section 419 outputs a RAT detection result.

Embodiments 1 to 3 of the present invention have been explained.

In this way, according to Embodiments 1 to 3, the relay station of awideband communication system including LTE covers an identical coveragearea to a coverage area of a narrowband communication system includingWLAN and WiMAX. Then, the relay station of a wideband communicationsystem adds either a frequency offset, a time offset or a power offsetas information showing that the mobile station, which receives a relaysignal from the relay station, is located in the coverage area of anarrowband communication system, to a signal received from the basestation of the wideband communication system, and relays the resultingsignal. Therefore, according to Embodiments 1 to 3, in a mobilecommunication system where a plurality of RATs mix, it is possible makea control channel for reporting RAT information unnecessary and it ispossible to prevent capacity of a control channel from becoming tight orinsufficient.

Further, according to Embodiments 1 to 3, the mobile station can detectthe coverage area of a narrowband communication system using a relaysignal in a wideband communication system, and therefore, when themobile station detects the coverage area of each RAT, the mobile stationdoes not need to communicate using a control channel or narrowbandcommunication system. That is, according to Embodiments 1 to 3, themobile station can detect the coverage area of a narrowbandcommunication system without switching to communication using a controlchannel or switching to communication using the narrowband communicationsystem. Therefore, according to Embodiments 1 to 3, the mobile stationcan reduce power consumed by a process of detecting the coverage area ofa narrowband communication system. Further, the mobile station canshorten the time it takes to detect the coverage area of a narrowbandcommunication system.

Further, according to Embodiments 1 to 3, in the mobile station, it ispossible to diversity-combine a signal received directly from the basestation of a wideband communication system and a relay signal from therelay station of the wideband communication system, so that it ispossible to provide diversity effect. Therefore, according toEmbodiments 1 to 3, it is possible to improve reception performance ofthe mobile station.

Embodiment 4

In the above Embodiments 1 to 3, LTE base station 10 reports to mobilestation 40 using a broadcast channel in advance what information mobilestation 40, which has detected the coverage area of a narrowbandcommunication system, needs to report to LTE base station 10.Information requested to report to LTE base station 10 when mobilestation 40 detects the coverage area of a narrowband system includemobile station ID, RAT detection result and a communication status ofmobile station 40.

When mobile station 40 detects the coverage area of a narrowbandcommunication system using a relay signal in a wideband communicationsystem, mobile station 40 reports information requested in advance fromLTE base station 10, to LTE base station 10.

By this means, necessary information is sequentially reported to LTEbase station 10 from mobile station 40 located in the coverage area of anarrowband communication system, so that it is possible to controltraffic using not only coverage area information of a widebandcommunication system but also coverage area information of a narrowbandcommunication system. For example, when mobile station 40 communicatingin a wideband communication system with heavy traffic is located in thecoverage area of a narrowband communication system with low traffic, LTEbase station 10 performs handover of mobile station 40 to the narrowbandcommunication system. Consequently, according to the present embodiment,LTE base station 10 can disperse traffic in the wideband communicationsystem and the narrowband communication system, and optimally controlthe overall traffic in the coverage area of LTE base station 10.Further, in mobile station 40, it is not necessary to switch a carrierfrequency or measure the power of a narrowband communication systemuntil mobile station 40 receives a handover command to a narrowbandcommunication system from LTE base station 10, so that it is possible toreduce the processing loads in mobile station 40.

Further, as described above, according to Embodiments 1 to 3, in mobilestation 40, it is possible to reduce the time it takes to detect thecoverage area of a narrowband communication system, so that, accordingto the present embodiment, mobile station 40 can report informationquickly to LTE base station 10, and consequently, following the trafficcontrol in LTE base station 10 improves.

Embodiments of the present invention have been explained.

The present invention may be implemented by combining the aboveembodiments.

Further, although cases have been explained above with the embodimentswhere one example of RATs of wideband communication systems is LTE andone example of RATs of narrowband communication systems is WLAN andWiMAX, the present invention does not limit the RAT of a widebandcommunication system to LTE. For example, other RATs of widebandcommunication systems include W-CDMA, LTE-Advanced or communicationsystems after LTE-Advanced. Further, the present invention does notlimit RATs of narrowband communication systems to WLAN and WiMAX. Forexample, other RATs of narrowband communication systems include LTE,LTE-Advanced or communication systems after LTE-Advanced, which are usedas hotspots.

Further, although cases have been explained with the above embodimentswhere part of the coverage area of a wideband communication systemincludes the entire coverage area of a narrowband communication systemand the part of the coverage area of the wideband communication systemoverlaps the entire coverage area of the narrowband communicationsystem, the present invention may be implemented as described above incases where part of the coverage area of a wideband communication systemincludes part of the coverage area of a narrowband communication systemand the part of the coverage area of the wideband communication systemoverlaps the part of the coverage area of the narrowband communicationsystem.

Further, a base station apparatus may be referred to as a “Node B” and amobile station apparatus may be referred to as a “UE.” Furthermore, therelay station according to the embodiments is referred to as “repeater,”“simple base station,” “cluster head,” and so on.

Further, although cases have been described with the above embodiment asexamples where the present invention is configured by hardware, thepresent invention can also be realized by software.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. These may be individualchips or partially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC,” “systemLSI,” “super LSI,” or “ultra LSI” depending on differing extents ofintegration. Further, the method of circuit integration is not limitedto LSIs, and implementation using dedicated circuitry or general purposeprocessors is also possible. After LSI manufacture, utilization of aprogrammable FPGA (Field Programmable Gate Array) or a reconfigurableprocessor where connections and settings of circuit cells within an LSIcan be reconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosures of Japanese Patent Application No. 2007-188572, filed onJul. 19, 2007, and Japanese Patent Application No. 2007-330837, filed onDec. 21, 2007, including the specifications, drawings and abstracts, areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, communicationsystems (for example, multihop systems) in which radio communicationapparatuses including mobile stations and base stations carry out radiocommunication via relay stations.

1. A base station apparatus configured to cover a first area includingpart or entirety of a second area using a first Radio Access Technology(RAT), the base station apparatus comprising: a transmitter configuredto transmit, to a mobile apparatus which belongs to the first area, arequest signal for request a transmission of notification informationwhen the mobile apparatus detects the second area using a second RATdifferent from the first RAT, and a receiver configured to receive thenotification information from the mobile apparatus using the first RAT.2. The base station apparatus according to claim 1, wherein the requestsignal is transmitted using a broadcast channel to the mobile apparatus.3. The base station apparatus according to claim 1, wherein thenotification information includes at least one of a ID of mobileapparatus, a detection result by the mobile station, and a communicationstate at the mobile apparatus.
 4. A mobile apparatus that belongs to afirst area, which includes part or entirety of a second area and whichis covered by a base station apparatus using a first Radio AccessTechnology (RAT), the mobile apparatus comprising: a receiver configuredto receive, from the base station apparatus, a request signal forrequest a transmission of notification information to the base station,and a transmitter configured to transmit, to the base station apparatus,the notification information using the first RAT when the mobileapparatus detects the second area using a second RAT different from thefirst RAT.
 5. The mobile apparatus according to claim 4, wherein therequest signal is received using a broadcast channel from the basestation apparatus.
 6. The mobile apparatus according to claim 4, whereinthe notification information includes at least one of a ID of mobileapparatus, a detection result by the mobile station, and a communicationstate at the mobile apparatus.
 7. A communication method performed by abase station apparatus configured to cover a first area including partor entirety of a second area using a first Radio Access Technology(RAT), the communication method comprising: transmitting, to a mobileapparatus which belongs to the first area, a request signal for requesta transmission of notification information when the mobile apparatusdetects the second area using a second RAT different from the first RAT,and receiving the notification information from the mobile apparatususing the first RAT.
 8. A communication method performed by a mobileapparatus that belongs to a first area, which includes part or entiretyof a second area and is covered by a base station apparatus using afirst Radio Access Technology (RAT), the communication methodcomprising: receiving, from the base station apparatus, a request signalfor request a transmission of notification information to the basestation, and transmitting, to the base station apparatus, thenotification information using the first RAT when the mobile apparatusdetects the second area using a second RAT different from the first RAT.